Kô Nakahira - Mikkai AKA The Assignation (1959)

This well-paced, effective drama by director Ko Nakahira eloquently decries the foibles of adultery by looking at a worst possible scenario. Young Kikuko (Yoko Katsuragi) is married to an older university professor and because of the age difference as well as several other factors, she is bored with the marriage and falls for one of his students, Yuichiro (Seiji Miyaguchi). The two manage to sneak off for stolen moments together and on one of those occasions in the park, they both witness a murder. Shocked by what they saw, the student insists that they immediately go to the police to testify against the killer. But this is Japan, after all, and the adulterous wife knows that losing face by losing her marriage over her infidelity is much worse than the need to identify a killer. Unfortunately for him, the student never quite sees it her way.
~ Eleanor Mannikka, Rovi